Presenter/Author Information

Type of Presentation

Oral

Session Title

Utilizing Green Infrastructure to improve Water Quality and Environmental Outcomes in the Urban Realm

Description

In 2009 King County Wastewater Treatment Division (KCWTD) selected green stormwater infrastructure (GSI) as the preferred alternative for controlling combined sewer overflows (CSO) for the 1100-acre Barton combined sewer system (CSS) basin in Seattle. In 2008 KCWTD reported that the basin had an average of four overflows per year that discharge a total of four million gallons into Puget Sound. In order to reduce the overflows to no more than one CSO event per year for Washington State’s Department of Ecology compliance, KCWTD retrofitted 15 residential streets with bioretention cells in order to intercept, treat and reduce the amount of stormwater discharging into the CSS. After filtering through the bioretention soil and plantings, stormwater discharges into an underdrain that conveys the flows into an underground injection control screen well for deep infiltration to a receptive soil layer beneath the area’s glacial till. Intercepting stormwater before it enters the CSS will reduce KCWTD’s annual treatment plant costs. The project completed construction of the first ten streets in 2014 and the remaining five streets in 2015. Our presentation will cover challenges confronted by this pioneering project (the first for KCWTD) from planning, design, community outreach, construction and through the first two years of operations and maintenance. We will also review how we balanced CSO control performance with community concerns and street performance so issues such as slope, planter width, existing utilities and trees, access, and on-street parking patterns were key design drivers; how KCWTD developed and implemented a new maintenance program for the wastewater treatment division; and how the team developed infrastructure that met current needs while incorporating flexibility to respond to an uncertain future and changing climate. Finally, we will provide the latest results in monitoring for CSO events in the basin for the first two years of operation and maintenance.

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In 2009 King County Wastewater Treatment Division (KCWTD) selected green stormwater infrastructure (GSI) as the preferred alternative for controlling combined sewer overflows (CSO) for the 1100-acre Barton combined sewer system (CSS) basin in Seattle. In 2008 KCWTD reported that the basin had an average of four overflows per year that discharge a total of four million gallons into Puget Sound. In order to reduce the overflows to no more than one CSO event per year for Washington State’s Department of Ecology compliance, KCWTD retrofitted 15 residential streets with bioretention cells in order to intercept, treat and reduce the amount of stormwater discharging into the CSS. After filtering through the bioretention soil and plantings, stormwater discharges into an underdrain that conveys the flows into an underground injection control screen well for deep infiltration to a receptive soil layer beneath the area’s glacial till. Intercepting stormwater before it enters the CSS will reduce KCWTD’s annual treatment plant costs. The project completed construction of the first ten streets in 2014 and the remaining five streets in 2015. Our presentation will cover challenges confronted by this pioneering project (the first for KCWTD) from planning, design, community outreach, construction and through the first two years of operations and maintenance. We will also review how we balanced CSO control performance with community concerns and street performance so issues such as slope, planter width, existing utilities and trees, access, and on-street parking patterns were key design drivers; how KCWTD developed and implemented a new maintenance program for the wastewater treatment division; and how the team developed infrastructure that met current needs while incorporating flexibility to respond to an uncertain future and changing climate. Finally, we will provide the latest results in monitoring for CSO events in the basin for the first two years of operation and maintenance.